In numerous techniques, solid particles are sent to a utilization station in a carrier or conveying gas. Thus, numerous processes of combustion use an injection of combustible solid in pulverized form conveyed by a gas, typically air or nitrogen. At the utilization station, it is frequently desirable to treat the particles in another gaseous environment than the conveying gas. For example, in combustion processes, the outputs are greatly improved by enrichment of the combustible with oxygen. Thus, the combustion of pulverized carbon injected into a blast furnace is greatly improved in the presence of air enriched with oxygen or pure oxygen. However, in a continuous process, it is not possible to burn the pulverulent solid without diluting the combustible with the conveying gas. In particular, the combustion in pure oxygen of the carbon is impossible if the supply device .for the pulverized solid does not also operate with pure oxygen, which is impossible for safety reasons. Another problem resides in the time necessary for the mixing in situ of the flow of solid particles with the combustible gas. In practice, a dense jet of pulverulized solid disperses poorly and a portion of the particles is not contacted with the combustible gas under the required conditions.